Induction of type II T4-5'-monodeiodinase activity in brown adipose tissue in fasted mice.
In order to study the effect of starvation on brown adipose tissue (BAT) type II 5'-monodeiodinating activity (5'MDI), type II 5'MDI was measured in vitro in the presence of 20 mM dithiothreitol, 1 mM propylthiouracil, 2 nM thyroxine (T4) and appropriate amounts of 600 X g infranatant of BAT from fed control or 3 day fasted mice, with or without daily T4 replacement (1.2 micrograms/100 g bw) during starvation. I- released from 125I-T4 was measured by ion-exchange column chromatography. Activity of BAT 5'MDI was markedly elevated in the 3 day fasted group (133 +/- 28 fmol I-/h per mg protein vs. 26 +/- 6.4; p less than 0.05). Kinetic studies using BAT infranatant suggested that fasting-induced activity is associated with a similar change in the Vmax, but no demonstrable change in apparent Km of T4 monodeiodination. T4 replacement during fasting, which normalized both serum T4 and T3 in fed and 3 day fasted groups, did not stop the increase of BAT 5'MDI in the fasted group (p less than 0.01). The data suggest that: (1) the fasting-induced increase in BAT 5'MDI is due mainly to the changes in capacity rather than the affinity of the enzyme, and (2) the fasting-induced increase in BAT 5'MDI is not mediated entirely through changes in serum thyroid hormone concentration.
Wu
S Y
SY
Nuclear Medicine and Medical Services, Veterans Administration Medical Center, Long Beach, California.
Wright
C
C
Parker
L N
LN
Florsheim
W
W
D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D004229:Dithiothreitol / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005215:Fasting / Q000502:physiology*; D005260:Female; D007453:Iodide Peroxidase / Q000096:biosynthesis*; D007700:Kinetics; D051379:Mice; D011441:Propylthiouracil / Q000494:pharmacology; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D011441:Propylthiouracil; D007453:Iodide Peroxidase; D013974:Thyroxine; D004229:Dithiothreitol